With the recent proliferation of portable electronic apparatuses such as mobile phones and electronic organizers, a need has arisen for recharging and data transfer stations (hereinafter referred to simply as ‘station(s)’). Such stations are commercially available and are designed to enable electronic apparatus users to both recharge devices and carry out data transfer. There are differing designs and methods of operation for such stations. In the conventional art, either electrical contacts or a coil are employed. Use of electrical contacts enables the structure of the apparatus to be kept relatively simple, but prevents the apparatus from being able to be sealed, whereby the water resistance of the apparatus cannot be obtained.
A station for recharging and data transfer which is equipped with a coil can be used for the above purpose with an electronic apparatus which is also equipped with a coil. When data transfer or recharging a battery is to be carried out between the station and the electronic apparatus, a high frequency signal is fed to a coil of one side, thereby inducing a magnetic field around the coil. This magnetic field induces an electric current in a coil of the other side. By rectifying the induced current and then feeding it to a battery, the battery is recharged. Also, extracting signals from the induced current enables transfer of data.
When a portable electronic apparatus, using a rechargeable (or a primary) battery as a power supply, has high load devices which consumes large power of the battery, battery voltage may be lowered significantly when the high load device is driven.
Such high load devices include, for example, a vibrator motor that is used for notification, an electroluminescence (EL) display for displaying information, and a flash memory which consumes large amount of power when writing and erasing data.
These high load devices significantly lower battery voltage when the devices are driven. Therefore, the battery must have enough charge and the internal resistance of the battery has to be low in order to correctly drive these high load devices.
Furthermore, when a high load device is driven and the battery voltage is lowered below the system requirement, the system fails, and requires resetting.
In order to solve the above drawbacks, a Japanese patent application laid-open No. H11-259190 discloses a control method for a portable terminal with a high load device. In this method, battery voltages without a load and with a certain load are measured, and then the internal resistance of the battery is calculated. Then using the calculated internal resistance and a load characteristic of the high load device, a predicted battery voltage is calculated for a case when the high load device is driven. Then a judgement is made whether the battery voltage would be lowered below a lowest voltage for driving the portable electric device when the high load device is driven. When driving the high load device would not lower the battery voltage below the lowest voltage for driving the portable electronic appliance, the high load device can be driven.
Below, the calculation method disclosed in the Japanese patent application laid-open No. H11-259190 is explained.
When a voltage of a battery under no load is V0 (Volt) and the battery voltage with a certain resistor R (Ω) being connected as a dummy load is V1 (volt), an internal resistance r (Ω) of the rechargeable battery can be obtained from the following equation,r=R·(V0−V1)/V1.
Also, when a predicted value of the battery voltage with an actual high load device being connected is V3 (volt) and the necessary power for driving the high load device is P (watt), the following equation is obtained,V3=[V0+√(V02−4rP)]/2
When this predicted value of the battery voltage V3 satisfies the following inequality, the high load device can be driven.V3≧V4
Where V4 is a lowest operational voltage for driving the portable terminal.
A drawback of this prior art method, however, is the need to complete a complicated calculation before actually driving a high load device. Completion of such a calculation is time-consuming, making it difficult to apply the method, to, for example, an EL display. Namely, when controlling an EL display, rapid judgement must be made to determine whether using the EL display is possible.
Also, in order to obtain a calculation result rapidly, an calculation circuit is subject to a high load, whereby power consumption is increased.
Also, the above conventional method does not allow a high load device to be connected directly to a battery that is a preceding step of constant voltage circuit.
Also, even when a device can work below the rated output voltage of the constant voltage circuit, if the output voltage of the constant voltage circuit declines below the rated output voltage, the system fails first, and the device can not be driven.